# std::overflow_error

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Defined in header `<stdexcept>` |  |
class overflow_error; |  |

Defines a type of object to be thrown as exception. It can be used to report arithmetic overflow errors (that is, situations where a result of a computation is too large for the destination type).

The only standard library component that throws this exception is std::bitset::to_ulong. | (until C++11)
The only standard library components that throw this exception are std::bitset::to_ulong and std::bitset::to_ullong. | (since C++11)

The mathematical functions of the standard library components do not throw this exception (mathematical functions report overflow errors as specified in math_errhandling). Third-party libraries, however, use this. For example, boost.math throws `std::overflow_error` if `boost::math::policies::throw_on_error` is enabled (the default setting).

Inheritance diagram

### Member functions

(constructor) | constructs a new `overflow_error` object with the given message (public member function)
operator= | replaces the `overflow_error` object (public member function)

## std::overflow_error::overflow_error

overflow_error( const std::string& what_arg ); | (1) |
overflow_error( const char* what_arg ); | (2) |
overflow_error( const overflow_error& other ); | (3) | (noexcept since C++11)

1) Constructs the exception object with what_arg as explanatory string. After construction, std::strcmp(what(), what_arg.c_str()) == 0.
2) Constructs the exception object with what_arg as explanatory string. After construction, std::strcmp(what(), what_arg) == 0.
3) Copy constructor. If *this and other both have dynamic type `std::overflow_error` then std::strcmp(what(), other.what()) == 0. No exception can be thrown from the copy constructor.

### Parameters

what_arg | - | explanatory string
other | - | another exception object to copy

### Exceptions

1,2) May throw std::bad_alloc.

### Notes

Because copying `std::overflow_error` is not permitted to throw exceptions, this message is typically stored internally as a separately-allocated reference-counted string. This is also why there is no constructor taking `std::string&&`: it would have to copy the content anyway.

Before the resolution of LWG issue 254, the non-copy constructor can only accept std::string. It makes dynamic allocation mandatory in order to construct a std::string object.

After the resolution of LWG issue 471, a derived standard exception class must have a publicly accessible copy constructor. It can be implicitly defined as long as the explanatory strings obtained by `what()` are the same for the original object and the copied object.

## std::overflow_error::operator=

overflow_error& operator=( const overflow_error& other ); |  | (noexcept since C++11)

Assigns the contents with those of other. If *this and other both have dynamic type `std::overflow_error` then std::strcmp(what(), other.what()) == 0 after assignment. No exception can be thrown from the copy assignment operator.

### Parameters

other | - | another exception object to assign with

### Return value

*this

### Notes

After the resolution of LWG issue 471, a derived standard exception class must have a publicly accessible copy assignment operator. It can be implicitly defined as long as the explanatory strings obtained by `what()` are the same for the original object and the copied object.

## Inherited from std::runtime_error

## Inherited from std::exception

### Member functions

(destructor) [virtual] | destroys the exception object (virtual public member function of `std::exception`)
what [virtual] | returns an explanatory string (virtual public member function of `std::exception`)

### Example

Run this code

    #include <iostream>
    #include <limits>
    #include <stdexcept>
    #include <utility>

    template<typename T, int N>
        requires (N > 0) /*...*/
    class Stack
    {
        int top_{-1};
        T data_[N];

    public:
        [[nodiscard]] bool empty() const { return top_ == -1; }

        void push(T x)
        {
            if (top_ == N - 1)
                throw std::overflow_error("Stack overflow!");
            data_[++top_] = std::move(x);
        }

        void pop()
        {
            if (empty())
                throw std::underflow_error("Stack underflow!");
            --top_;
        }

        T const& top() const
        {
            if (empty())
                throw std::overflow_error("Stack is empty!");
            return data_[top_];
        }
    };

    int main()
    {
        Stack<int, 4> st;

        try
        {
            [[maybe_unused]] auto x = st.top();
        }
        catch (std::overflow_error const& ex)
        {
            std::cout << "1) Exception: " << ex.what() << '\n';
        }

        st.push(1337);
        while (!st.empty())
        	st.pop();

        try
        {
            st.pop();
        }
        catch (std::underflow_error const& ex)
        {
            std::cout << "2) Exception: " << ex.what() << '\n';
        }

        try
        {
            for (int i{}; i != 13; ++i)
                st.push(i);
        }
        catch (std::overflow_error const& ex)
        {
            std::cout << "3) Exception: " << ex.what() << '\n';
        }
    }

Output:

    1) Exception: Stack is empty!
    2) Exception: Stack underflow!
    3) Exception: Stack overflow!

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 254 | C++98 | the constructor accepting const char* was missing | added
LWG 471 | C++98 | the explanatory strings of `std::overflow_error`'s copies were implementation-defined | they are the same as that of the original `std::overflow_error` object

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